Patent GB-1213441-A (GB)
Title: Improvements in fibrous products
IPC: D04H3/16
Filed: 1969-01-02
Abstract: 1,213,441. Fibrous structures; laminated fibrous material. CELANESE CORP. 2 Jan., 1969 [4 Jan., 1968 (2)], No. 268/69. Addition to 1,190,639. Heading B5B, B5N. [Also in Divisions B2 and D1] A fibrous product of increased strength per unit weight is made by stretching a fibrous product made by the process of Specification 1,190,639, to elongate filament lengths between points of adhesion of the filamentary material constituting the product without rupturing the product. Specification 1,190,639, discloses the production of a body of entangled filamentary material by extruding a molten fibre-forming material through an orifice into a zone in which the molten material solidifies into a substantially continuous filament and attenuating the extrudate before it solidifies by the action of a plurality of high velocity gas or vapour streams flowing through passages arranged to direct the streams towards without intersecting the extrusion axis which forms, with the projection of each passage axis on the plane which includes the extrusion axis and the point on the passage axis at the passage outlet, an angle of 3 to 15 degrees. Specification 1,190,639, also discloses collecting the body of entangled filamentary material on a surface arranged close enough to the extrusion orifice for the collected material to be in a partly solidified adhesive condition, and, if desired, continuously removing the fibrous product so made from the zone in which it is formed. The present Specification discloses stretching, suitably so effected as to increase the surface area of the product to up to 15 times its original area; stretching may be effected in two directions normal to each other so as to achieve a 2 to 5 times increase in length in each direction, and, if desired, in stages with heat relaxation between stages. The use of polypropylene is exemplified. In Fig. 2, a biaxial elongation mechanism operates in an air heated chamber 20. Clamp means 24 which grasp the fibrous product 22 are moved in the directions of arrows X and Y and so elongate the product biaxially. Thus in Example 5 a polypropylene fibrous sheet is elongated biaxially in the apparatus of Fig. 2, at an elongation ratio of 3À5 : 1 in both the X and Y directions, in hot air at 110‹ C. Alternatively, the fibrous product may be biaxially elongated in a continuous process by being drawn over a heated shoe, the various directional elongations being either simultaneous or successive. Thus in Example 1 a polypropylene fibrous product in ribbon form is elongated over a hot shoe at 120‹ C. to an elongation ratio of 3. Where stretching is effected in stages, the product may be heat relaxed after the first stretching stage at temperatures below the polymer melting point, using, e.g. radiant heat or a heated gas or liquid, superheated steam being preferred. Where first stage stretching is biaxial, the second stage stretching may be uniaxial or vice versa; this method is illustrated by Examples 6, 7 and 8. Laminated structures can be made, using, in general, the more dense fibrous products of the invention, by the use of thermoplastic or other adhesives, and the fibrous products may be laminated to metal foils, cellulosic or synthetic papers, isotropic or nonisotropic films of thermoplastic polymers, and other flexible sheet materials. Thus, in Example 2, two lengths of a stretched polypropylene fibrous product are cross-laminated by spraying on to one length an aqueous emulsion of low molecular weight polyethylene, laying the second length over the sprayed material so that their directions of elongation are at approximately right angles, and uniting the cross-laminate in a heated press. Example 4 describes the lamination of a stretched polypropylene fibrous product to a polyethylene film by heating in a press.